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Abstract:

A side-coupling optical fiber assembly comprises a first substrate (200),
on a surface of which at least one concave groove is provided; an optical
fiber (210) disposed in the concave groove; and a second substrate (220)
disposed on the first substrate (200) and pressed on the optical fiber
(210). The end of the optical fiber (210) between the first substrate
(200) and the second substrate (220) is set as a slant surface (240),
which is used for performing total reflection for the light beam
transmitted in the optical fiber (210). A method for making the
side-coupling optical fiber assembly is provided.

Claims:

1. A side-coupling optical fiber assembly comprising: a first substrate
having at least one groove formed on one of its surfaces; an optical
fiber arranged in the groove; and a second substrate arranged above the
first substrate such that the second substrate presses and covers the
optical fiber; wherein an inclined facet is formed on the fiber end
positioned between the first and the second substrates, the inclined
facet being for realization of a total internal reflection of the light
beam transmitted in the optical fiber.

2. The side-coupling optical fiber assembly of claim 1 wherein the first
and the second substrates are fixed together.

3. The side-coupling optical fiber assembly of claim 2 wherein one end
edge facet of each of the first and second substrates is in the same
surface of the inclined end facet of the optical fiber.

4. The side-coupling optical fiber assembly of claim 3 wherein a first
light-passing hole is arranged in the second substrate, the first
light-passing hole corresponding to the path of the light beam after the
light beam is totally reflected from the inclined end facet of the
optical fiber; or wherein the second substrate is made of an identical or
similar material as that of the waveguide of the optical fiber.

5. The side-coupling optical fiber assembly of claim 1 wherein the second
substrate is an extended optical bench, wherein at least one optical
element is arranged on the second substrate.

6. The side-coupling optical fiber assembly of claim 5 wherein the
optical element arranged on the second substrate is a lens, the
transmission region of the lens corresponding to the projection region of
the totally reflected light beam.

7. The side-coupling optical fiber assembly of claim 6 further comprising
a spacer plate arranged above the second substrate, wherein a slot hole
is arranged in the spacer plate and the lens is adapted to the slot hole.

8. The side-coupling optical fiber assembly of claim 7 further
comprising: a mounting substrate for an optical receiving chip, wherein
the mounting substrate is arranged above the spacer plate, and wherein a
second light-passing hole is arranged in the mounting substrate and
corresponds to the projection region of the light beam after through the
lens; and an optical receiving chip arranged above the second
light-passing hole and combined with the mounting substrate.

9. A method of making a side-coupling optical fiber assembly, the method
comprising the steps of: putting an optical fiber into a groove formed on
a first substrate; fixing a second substrate to the first substrate by
means of adhesion such that the optical fiber losses all its degrees of
freedom; grinding or polishing the end face of the optical fiber and the
end edge faces of the first and the second substrates into one same
inclined surface such that a total internal reflection of the light beam
in the optical fiber takes place at the formed inclined end facet of the
optical fiber.

10. The method of claim 9 further comprising the step of keeping the
first and the second substrates in a horizontal position after they are
fixed together, wherein at least one additional optical fiber having the
same diameter as the said optical fiber is put in another groove of the
first substrate, after which the first and the second substrates are
fixed together.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a U.S. Nationalization of PCT International
Application No. PCT/CN2010/070505 filed Feb. 4, 2010, entitled "LATERALLY
COUPLED OPTICAL FIBER COMPONENT AND PROCESSING METHOD THEREOF," which
claims priority to Chinese Patent Application No. 200910130017.8 filed
Mar. 26, 2009, the entireties of both of the foregoing applications are
incorporated herein by reference.

TECHNICAL FIELD

[0002] This invention relates to an optical packaging technology for
optoelectronic devices. More specifically, this invention relates to a
side-coupling optical fiber unit for fiber packaging of semiconductor
optoelectronic devices and a fabrication method thereof in the field of
fiber optic communication.

BACKGROUND

[0003] For optoelectronic devices applied to transmitting or receiving
optical signals or energies, much optical transmission between the device
and the outside needs be realized through optical fibers (or in short
"fibers" hereof), therefore, an optical coupling issue exists in these
optoelectronic devices between a photoelectric conversion element, which
is the key part of the device, and the optical fiber. This is called the
fiber packaging of the optoelectronic devices.

[0004] Please refer to FIG. 1, which shows the working principle of the
side-coupling optical fiber unit from under the prior art. That is, the
input and the output of the light beam at the end of the optical fiber is
not along the axial direction of the fiber but the radial direction,
i.e., at a right angle to the fiber axis. The side coupling is realized
through an inclined end facet formed on the optical fiber end 140, which
satisfies a total-internal-reflection condition. The side-coupling
structure is normally used in coupling of an optical fiber to a
surface-type photoelectric conversion element 100 under a certain
packaging mode, more commonly seen as between an optical fiber 110 and a
surface-type semiconductor optical-receiver chip in a butterfly package.

[0005] Please refer to FIG. 2, which illustrates the typical embodiment of
the above side-coupling optical fiber unit in the prior art. The fixing
of the fiber 110 at a spatial position is realized through a generally
metallic package 150 that contains the photoelectric conversion element
100. A circular through-hole 160 for passing the fiber is arranged in the
package 150, and a certain section of the fiber 110 is fixed in the
through-hole 160. A typical fixation process is to tightly attach a metal
sleeve layer 170 to a naked fiber 110, whose outer protective materials
have been removed, and to solder the fiber 110 with the attached metal
sleeve layer 170 into the through-hole 160 by metallic solders, wherein
the process forms an airtight and stable packaging.

[0006] In the side-coupling structure of the prior art, the optical fiber
needs be placed above the surface-type photoelectric conversion element,
due to the following two main reasons:

[0007] (1) The structure that the working (coupling) surface of the
photoelectric conversion element is being upward and the fiber end is
above the working surface is easy for observation and alignment. The
effective working region of the working surface of the photoelectric
conversion element is generally a limited round region 120 circled by a
metallic ring electrode 130 (as shown in FIG. 1). The observation and the
alignment are handled under a microscope.

[0008] (2) The lead electrode 130 of the photoelectric conversion element
is generally situated on the same surface of the working surface of the
element (as shown in FIG. 1), and electrical connections between this
lead electrode and the electrode of the mounting substrate of the
element, between electrodes of all elements, and between an electrode of
an element and the package frame, are generally realized through wire
bonds, the wire being generally an ultrathin gold wire and the bonds
formed by professional wire bonding machines, wherein the wire bonding
process requires that each electrode surface be in an upward position.
This necessitates also the upward positioning of the working surface of
the photoelectric conversion element.

[0009] In the prior art, although the structure that the optical fiber is
positioned above the photoelectric conversion element is easy for
observation and alignment, a stability issue of the fiber fixation comes
into existence due to the way of fiber fixing. The problem begins to show
up when the working region of the photoelectric conversion element
becomes very small. For a semiconductor optoelectronic chip used in the
optical receiving in the optical communication, the size of the working
region directly affects the working speed of the chip, as the higher the
speed, the smaller a designed working region is to be needed. In the
prior art, for the fiber fixing is not directly made to the fiber end but
to a certain limited section some distance away from it, the fiber end
can have quite a large spatial freedom. Particularly, for a slight angle
of tilting of the fixed section, a relatively large displacement can
occur at the fiber end. Moreover, the fiber fixing utilizes metallic
elements which are in nature with large thermal expansion and contraction
effects, including the unevenly distributed metallic solder materials,
wherein this metalized, soldering process is needed for an airtight
packaging. Hence, the fiber end is easy to drift away from its original
optimal coupling position, for a slight movement of the fixed section of
the fiber resulting from stress variation in the soldering part due to
such as the temperature change, which then leads to device performance
degradation or even fail.

[0010] At the unit channel speed reaching 10 G (1 G=109) bits per
second applied in current optical communication systems, the diameter of
the working region of a semiconductor optoelectronic chip for the optical
receiving has shrank to as small as 30 μm. As the speed increases to
the next grade of 40 G, the diameter will further decrease to 12 μm,
whereas the diameter of the light beam propagated in a conventional
single-mode fiber is already about 10 μm. Therefore, with the increase
of the speed, the optical coupling becomes more and more sensitive to the
position shift of the fiber. In current 10 G-dominated industrial product
developments and production practices, problems out of this coupling
instability such as reliability hard to be achieved, low primary
qualification rate, and too long manufacturing time have already been in
existence, making a production difficult to enter high volume, together
with a high cost.

[0011] On the other side, while the speed goes up to higher grades,
requirements on the electrical packaging of the optoelectronic devices
also grow. The impeding and parasitic effects brought by the bonding wire
on high-frequency electrical signals become stronger with the increase of
signal frequency, and to a certain stage the performance becomes
remarkably deteriorated. In theory, the situation of frequency upgrade
can be accommodated by reducing the wire length. However, due to
limitation of the wire bonding process wherein the wire length can not be
decreased permanently, when the signal wire reaches as short as 100
μm, the employing of the wire bonding technology becomes quite
difficult. This situation basically corresponds to a wire length
requirement when the speed reaches 40 Gb/s.

[0012] An effective solution is to adopt the flip-chip mounting
technology, wherein the lead electrode of a chip element faces downward
and is directly bonded to the electrical circuit on the submount or
substrate by such as a commonly used soldering method with some solder
materials. As such, the connection lengths are made at a minimum, and
thereby it is able to meet the high-speed requirement. Meanwhile, the
flip-chip structure also provides advantages as improvement in heat
dissipation, increase of electrical connection density, etc. The
flip-chip mounting is already an established process in the
microelectronics field. As for an optoelectronic element, a main type
being that the lead electrode and the working surface for the optical
coupling are on the same surface, if the flip-chip technology is to be
adopted, the working surface will need be positioned downward, which is
incompatible with the conventional fiber packaging technology. Since the
positioning and the fixing of the optical fiber are done with the
through-hole structure of the package in the prior art, all fiber
coupling processes need rely on this package. This makes the coupling of
the optical fiber placed below a photoelectric conversion element whose
working surface is positioned downward difficult to conduct, for the
fiber is invisible in manipulation. As a result, the current fiber
packaging technology has restricted the implementation of the flip-chip
technology which otherwise could be adopted in many optoelectronic
devices.

Invention Contents

[0013] This invention aims to provide a side-coupling optical fiber
assembly and the fabrication method thereof for overcoming the defects
described above in the prior art.

[0014] For this purpose, the invention first provides a side-coupling
optical fiber assembly that comprises a first substrate, an optical
fiber, and a second substrate, wherein at least one groove is formed on
one surface of the first substrate, the optical fiber is arranged in the
groove, and the second substrate is arranged above the first substrate,
pressing and covering the optical fiber.

[0015] Among them, an inclined facet is formed on the fiber end positioned
between the first and the second substrates. The inclined facet is to
realize a total internal reflection of the light beam transmitted in the
optical fiber.

[0016] The first and the second substrates are fixed together to ensure
that the optical fiber between them loses all its degrees of freedom.

[0017] Preferably, one end edge facet of each of the first and the second
substrates is in the same surface of the inclined end facet of the
optical fiber.

[0018] A first light-passing hole is arranged in the second substrate,
corresponding to the path of the light beam after it is totally reflected
from the inclined end facet of the optical fiber; or, this second
substrate is made of an identical or similar material as that of the
waveguide of the optical fiber for reducing the internal reflection.

[0019] Preferably, the second substrate is an extended optical bench, and
at least one optical element is installed on it.

[0020] The optical element installed on the second substrate can be a
lens, and the transmission region of the lens corresponds to the
projection region of the totally reflected light beam.

[0021] Preferably, the side-coupling optical fiber assembly includes a
spacer plate. The spacer plate is arranged above the second substrate. A
slot hole is arranged in the spacer plate and the lens is adapted to the
slot hole.

[0022] Preferably, the side-coupling optical fiber assembly includes a
mounting substrate of an optical receiving chip, a second light-passing
hole, and an optical receiving chip, wherein the mounting substrate is
arranged above the spacer plate, the second light-passing hole is
arranged in the mounting substrate and corresponds to the projection
region of the light beam after through the lens, and the optical
receiving chip is arranged above the second light-passing hole and is
combined with the mounting substrate.

[0023] Second, the invention provides a fabrication method of the
side-coupling optical fiber assembly, which comprises the following
steps:

[0024] an optical fiber is put into a groove formed on a first substrate;

[0025] the first substrate and a second substrate are fixed together by
means of adhesion, which makes the optical fiber lose all its degrees of
freedom;

[0026] the end face of the optical fiber and the end edge faces of the
first and the second substrates are ground or polished into one same
inclined surface, wherein a total internal reflection of the light beam
in the optical fiber takes place at the formed inclined end facet of the
fiber.

[0027] In accordance, there's a step to keep the first and the second
substrates in a horizontal position after they are fixed together, as
follows:

[0028] at least one additional optical fiber having the same diameter as
the aforementioned optical fiber is put into another groove of the first
substrate, after which the first and the second substrates are fixed
together.

[0029] In comparison with the prior art, this invention has the following
advantages:

[0030] first, as a side-coupling optical fiber unit, it provides a direct
and complete confinement of the coupling optical fiber end, and in
combination with a mounting substrate of the photoelectric conversion
element, it is able to realize a stable and reliable lateral fiber
coupling under rigorous requirements;

[0031] second, the side-coupling optical fiber assembly of the invention
is flexible in installation, and it's convenient for accommodating
various kinds of packaging technologies including the flip-chip mounting;

[0032] last, the side-coupling optical fiber assembly of the invention can
provide a new assembling platform, upon which it can be extended to a
function-versatile, all-in-one side-coupling optical fiber assembly
including being implemented as a complete element mounting platform.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1 is a perspective view showing the working principle of the
side-coupling optical fiber unit from under the prior art.

[0034] FIG. 2 is a perspective view of the embodiment of the side-coupling
optical fiber unit of the prior art.

[0035] FIG. 3 is a perspective view of Embodiment 1 of the side-coupling
optical fiber assembly of this invention.

[0036] FIG. 4 is a side view of Embodiment 1 of the side-coupling optical
fiber assembly of this invention.

[0037] FIG. 5 is a perspective view of Embodiment 2 of the side-coupling
optical fiber assembly of this invention.

[0038] FIG. 6 is a side view of Embodiment 2 of the side-coupling optical
fiber assembly of this invention.

[0039] FIG. 7 is a side (and partially cross-sectional) view of Embodiment
3 of the side-coupling optical fiber assembly of this invention.

DETAILED DESCRIPTION

[0040] With the drawings, the above and other technical features and
advantages of the invention are further detailed below.

[0041] Please refer to FIGS. 3 and 4, which illustrate Embodiment 1 of the
side-coupling optical fiber assembly of the invention in a perspective
and a side view, respectively. The side-coupling optical fiber assembly
of the invention comprises: a first substrate 200, an optical fiber 210,
and a second substrate 220, wherein the first substrate 200 has at least
one groove, the optical fiber 210 is positioned in the groove, and the
second substrate 220 is placed above the groove substrate 200 pressing
down and covering the optical fiber 210 in the groove. The shape of the
groove needs to enable a simultaneous contact of the inserted optical
fiber 210 to both the side walls of the groove, and at the same time to
expose a certain portion of the fiber above the groove substrate surface
in order that the optical fiber can be in contact with the second
substrate 220. Under confinements from both the side walls of the groove
and the second substrate 220, the optical fiber 210 is completely
restricted in the groove. Under general circumstances, the optical fiber
210 here is a naked fiber, whose protective layers such as the outer
coating, the plastic sleeve, etc. are removed and internal waveguide
fiber exposes. As for the standard single-mode fiber, the internal
waveguide fiber material is quartz, and the waveguide fiber diameter is
125 μm.

[0042] The second substrate 220 and the first substrate 200 can be fixed
together by means of adhesion, for example simply by an ultraviolet
adhesive 230 which solidifies under an ultraviolet illumination after
dispensed and tightly combines each part. Under a tight connection
through the adhesive fixing, the degrees of freedom of the optical fiber
210 in the groove are totally lost. These include translation of the
optical fiber 210 along the axial direction of the groove and rotation
about its own axis. Hence the position and the status of the fiber end
240 are totally determined by the side-coupling optical fiber assembly.

[0043] One important feature of the side-coupling optical fiber assembly
of the invention is that the end face 240 of the fiber 210 is made into
an inclined facet which meets the total-internal-reflection condition,
and thus turns the light traveling along the axial direction of the fiber
210 into a lateral direction at the fiber end. The orientation of this
inclined facet is such that the lateral travelling light appears by the
side of the second substrate 220. In principle, a light-passing hole or
slot can be formed in the second substrate 220 so that the light beam
simply passes by the substrate instead of inside through; or, the second
substrate can even expose an entire section above the fiber end 240
position. However, due to overflow of the adhesive, there's always an
inevitable contamination of the fiber end. A simple and feasible way is
to use a same or similar material as that of the waveguide fiber 210 for
the second substrate 220, and at the same time to use an adhesive 230 of
a refractive index matching that of the waveguide fiber 210 and that of
the second substrate 220, together with a low absorption, these materials
and products being both actually available, and then to have the second
substrate 220 completely press and cover the fiber 210. Since the
refractive indexes of all parts are approximate, the light beam travels
as if it is in a homogeneous substance and there won't be much internal
reflection loss or influence. For the case that the light beam passes
through the upper surface of the second substrate 220, it is like the
normal axial input or output at an optical fiber end wherein the
reflection influence at the fiber end can either be counted or an
anti-reflection coating can be applied for reducing the reflection.

[0044] The angle θ of the fiber end facet 240 is determined in
accordance with the critical angle condition of the total internal
reflection at the interface formed by the waveguide fiber material and
its surrounding medium. When the incident angle of the light beam in the
optical fiber 210 to this end surface is any bit larger than the critical
angle, total internal reflection of the light beam will occur at this
surface, with no transmitted output. Hence, the value of θ is not
unique and can be selected according to some specific need such as output
direction, interfacial back-reflection influence, etc. As for the
quartz-air interface, the angle θ of the inclined fiber end facet
can be set at 42 degrees.

[0045] For the invention, the second substrate is an extended optical
bench, and at least one optical element can be installed on it. This is
another feature of significance of the invention.

[0046] Please refer to FIGS. 5 and 6, which illustrate Embodiment 2 of the
side-coupling optical fiber assembly of the invention in a perspective
and a side view, respectively. The capability of the extension owes to an
assembling-platform function that the second substrate 220 can actually
provide, in that other optical elements such as lenses, filters,
polarizers, reflecting mirrors, etc., can be readily installed and fixed
onto it, and some optoelectronic and electronic elements can also be
directly installed. In principle, the second substrate 220 provides a
function no more different from that of the mounting substrates generally
used in installation of various kinds of elements. A microlens 270 is
then to be added to the second substrate 220. The microlens is made by
semiconductor process, wherein the lens aperture can be made smaller than
1 mm, and the lens curvature is formed by photolithography and chemical
etching. This die-like microlens 270 has already been commercially
available. The lens materials include quartz and silicon, well suited for
transmission of the infrared lightwaves used in the fiber-optic
communication. The microlens 270 can be either a single-convex or a
double-convex type. In this embodiment the single-convex type is used so
that the lens is conveniently and directly installed onto the second
substrate 220 by using its planar base side, the installation being
simple and easy. An anti-reflection coating can be applied to both the
convex and the base side of the microlens 270 when needed, for reduction
of the reflection influence. The attachment between the microlens 270 and
the second substrate 220 can also be realized through index-matching
adhesive 230. In the installation, it is required that the light beam
output from the coupling fiber end 240 pass through the effective region
of the lens 270, therefore, there exists an issue of accurate alignment
of the lens 270 with respect to the central axial point of the fiber end
240. For this purpose, the end edge 250 formed on the upper surface of
the second substrate 220 in processing of the inclined end surface can be
utilized as an alignment guide. In addition, graphic alignment marks can
be designed and formed on the surface area outside the aperture region of
the die lens 270 by its semiconductor process. By using the graphic
alignment marks, in combination with the alignment guide edge 250, the
grooves, and else more as the locating references, the lens positioning
can be accurately done. Microlenses 270 with coatings and designated
alignment marks can both be supplied from the manufacturers under
correspondent customization services.

[0047] After addition of the microlens 270, a new, self-contained assembly
is formed upon the original optical fiber assembly. The addition of the
lens 270 will enhance control of the light transmission outside the
optical fiber 210. For instance, the light beam output from the fiber 210
has a nature of being divergent, whereas the lens 270 can act as a
converging element. This is very important to high-speed devices in which
the diameter of a light-receiving region is very small. For a
light-emitting element, such as the semiconductor laser diode used in the
optical communication, the emitted beam also has a nature of being
divergent, hence the lens can act with the same converging effect. When a
lens 270 is included, the thickness of the second substrate 220 becomes
an important parameter in controlling the overall optical characteristic
of the side-coupling optical fiber assembly.

[0048] Please refer to FIG. 7, which illustrates Embodiment 3 of the
side-coupling optical fiber assembly of the invention in a side view; it
is for fiber packaging of a high-speed optical receiving device in the
optical communication, wherein the optical receiving device comprises a
surface-type semiconductor optical receiving chip 100 and a mounting
substrate 300 of the chip. In order to fulfill the high-speed requirement
herein, the flip-chip technology is adopted in the electrical packaging
of the optical receiving chip 100, wherein the surface electrode of the
optical receiving chip 100 is directly bonded to a microwave transmission
circuit on the substrate 300 by solder alloy 310, whereas the working
surface of the optical receiving chip 100 for the optical coupling is
positioned downward facing toward the substrate 300. A second
light-passing hole 320, whose diameter is smaller than the chip 100 size
but far larger than the working region diameter of the optical receiving
chip of a high-speed application, is set at a corresponding position on
the substrate 300. For the case of a 40 Gb/s application, wherein the
working region of the optical receiving chip 100 is of a diameter of 12
μm, the second light-passing hole 320 can have a diameter of 200
μm.

[0049] As explained above, a die-type microlens 270 can also be added
here, which forms a new, extended side-coupling optical fiber assembly.
The thickness of the second substrate 220 then decides the distance
parameter in the object space of the lens 270. A spacer plate 330 is
adhered below to the substrate 300 of the optical receiving chip. A large
rectangular hole or slot 340 is formed in the spacer plate 330 in the
region corresponding to the second light-passing hole 320. In this way,
the upper surface of the second substrate 220 and the lower surface of
the spacer plate 330 can be adhered and fixed together with the microlens
270 on the second substrate 220 accommodated in the hole or slot 340 of
the spacer plate 330. This fiber-below-chip structure, where the working
surface of the optical receiving chip 100 is positioned downward, solves
the problem of the prior art that the fiber packaging is difficult to
coincide with the flip-chip mounting of the element. And in this
embodiment, the spacer plate 330 also controls the distance parameter in
the image space of the lens 270.

[0050] As in the above embodiment, the fiber packaging is actually
dissociated from the package 150 of the photoelectric conversion element.
The coupling and fixing processes between the side-coupling optical fiber
assembly and the substrate 300 having the optical receiving chip 100 can
both be done independently. In manipulation, the substrate 300 with a
receiving chip 100 installed can be turned over for the observation and
the alignment of the optical fiber coupling, and after being coupled and
fixed the substrate 300 and the fiber assembly are placed into the
package 150 together. At this moment, the fiber 210 still needs to go
through the through-hole 160 in the package 150, however, the fiber
fixing into the through-hole now concerns only the airtightness and the
mechanical strength of the packaging, no more related to the fiber
coupling. Furthermore, movements of the fixed section of the fiber in the
through-hole no longer affects the coupling status of the fiber. The
freedom of the fiber end 240 is totally restricted by the invented
side-coupling optical fiber assembly and the combined mounting substrate
300 of the optoelectronic chip. This direct fiber end fixing solves the
problem of poor coupling instability in the prior art, whereas the
coupling state in the prior art is easily affected by its fiber fixation
in the through-hole 160.

[0051] This invention then provides a fabrication method of the
side-coupling optical fiber assembly, which comprises the following
steps:

[0052] an optical fiber is put into a groove on a first substrate;

[0053] the first substrate and a second substrate are fixed together by
means of adhesion, which makes the fiber lose all its degrees of freedom;

[0054] the end face of the optical fiber and the end edge faces of the
first and the second substrates are ground or polished into one inclined
surface, wherein a total internal reflection of the light beam in the
optical fiber takes place at the inclined end facet of the fiber.

[0055] In reference to FIG. 4, the fiber end 240 is processed into a
required inclined facet with an angle θ and the inclined end facet
is strictly positioned in a required orientation relative to the groove.
The process begins with putting an unprocessed naked fiber 210 into the
groove, and then follows with fixing the second substrate 220, the fiber
210, and the first substrate 200 together by an adhesive 230. After that,
the common ends of the three are as a whole ground or polished into an
inclined surface at a required angle by using a special processing mould.
The grinding or polishing of the three in a whole not only eliminates the
need for considering the fiber 210's orientation when it is placed, but
also provides an important guide edge 250 formed during the process on
the upper surface of the second substrate 220, wherein the guide edge 250
acts as a good alignment reference with respect to the central axial
point of the optical fiber end 240. This is due to a fact that the
horizontal distance between this guide edge and the central axial point
of the fiber end 240 is always a constant that can be calculated. As the
size of the waveguide fiber is very small and its material is transparent
and uniform, it's hard to determine the precise fiber axis position with
naked eyes. Therefore, the existence of this guide edge 250 provides the
base for a structural and functional extension of the side-coupling
optical fiber assembly of the invention.

[0056] In disposition of the second substrate 220, it is important if the
upper surface of the substrate is positioned horizontally or not. This
concerns the traveling direction of the light beam after it passes
through the substrate. Therefore, in addition to the requirement that the
upper and lower surfaces of the second substrate 220 have a high level of
parallelism, multiple identical grooves can be formed in the first
substrate 200 and, identical auxiliary fibers 260 can be put in the
grooves, the length of which being limited and matching only that of the
grooves. With the auxiliary grooves and fibers, the lower surface of the
second substrate 220 can be put in a horizontal position when it is
adhered and fixed to the first substrate 200.

[0057] The above are only preferred embodiments of the invention, and they
are illustrative only, not restrictive. Personnel in the specific
technical field understand that many changes, modifications and even
equivalences can be made to these embodiments within the spirit and the
scope limited by the claims of the invention, but are all within the
protection of the invention.